The sensitivity of a balance generally changes over time as a result of environmental influence factors such as fluctuations of the temperature and the barometric pressure, and also due to aging of components. Balances should therefore be recalibrated on a regular basis.
Electronic balances are in many cases calibrated by means of an internal calibration weight. To perform a calibration, a calibration weight of a defined mass is brought into force-transmitting contact with the force-transmitting device that is arranged in a force-measuring cell of a balance, or with the force-receiving part of the force-measuring cell, and a reference value is established. Based on this reference value, further weighing parameters of the balance can be adjusted. After the calibration has been successfully completed, the calibration weight is separated again from contact with the force-transmitting device or the force-receiving part and is secured in a rest position. In this calibration cycle, a transfer mechanism moves the calibration weight from a rest position into a calibration position and back to the rest position. In the calibration position, the calibration weight is in force-transmitting contact with the force-measuring cell, specifically with the force-receiving part of the latter. In the rest position, there is no force-transmitting contact. The range of movement of the calibration weight is limited in both directions by mechanical elements. These elements can be constituted for example by the support bearings of the spindle shaft, if the transfer mechanism is driven by way of a threaded spindle as disclosed in EP 1873504 A1, or by neighboring elements of a cam disk, if the calibration weight is supported by a cam disk that is coupled to the drive system as described in EP 1674841 A1. These mechanical limiting elements are called end stops. The positions of the end stops are individual to each balance.
According to the known state of the art, the end stops can be equipped with mechanical switches. These switches are activated by the transfer mechanism when the latter moves against one of the end stops, whereby the drive system is switched off. Such switches have the disadvantage that they will wear down to some degree over time. Furthermore, the switching actions can give rise to stresses and dislocations in the switch itself or for example in the support bearing of a threaded spindle of the aforementioned kind.
However, an improvement is achieved if the position immediately before the end stop is detected by means of an electro-optical sensor. For example, a circular disk with a cutout is mounted on the axle of the drive system and works together with a light gate. When the light gate detects the cutout in the disk, the drive system is stopped. This solution also has the disadvantage that it requires a precise and time-consuming adjustment procedure.
The fact that the position of the calibration weight is in general unknown represents a further disadvantage of switches.
In a calibration arrangement that is disclosed in CH 676750 A5, the distance traveled by the calibration weight is measured with an electronic revolution counter at the motor or with a mechanical registration of the angle of rotation of a toothed gear of a transmission. This concept has the disadvantage that because of the inaccuracy of the revolution counter the position of the calibration weight can only be roughly estimated.
Compared to the existing technology, exemplary embodiments of the inventive concept introduces a method to adjust the rest position and calibration position in the most efficient way possible and to control the movement of the calibration weight along its entire travel range.
It is therefore the object of the present invention to adjust the rest position and the calibration position in the most efficient way possible and to control the movement of the calibration weight along its entire travel range.